ladysaaphire

I have a 2007 Chevy Impala 3900 with a bad oil pressure sensor that needs to be changed. I have seen a few diagrams of its location, on the internet, but I'm not exactly sure they're what I need or they're the correct diagrams.
I need to know exactly where it's located as well as how to get to it to change it. If the location described by the internet is correct I don't know how to get to it. Do I go from above or below? Is there a heat shield involved? I removed the upper heat shield once, but it's not behind it and appears as though it's behind the lower heat shield. Any help would be greatly appreciated.